Conventional insect-nets consist either of metal wires and are then used exclusively mounted onto a frame, or else of textile threads and which are used mainly as so called mosquito nets, i.e. one hangs the net above a rack or the like. The net is not subjected to mechanical strain and a relatively loose binding technique holds the individual threads in place.
The desire to reduce the use of and to a certain extent even the prohibition against using chemical insecticides within the greenhouse industry has entailed so that the demand of locking out of harmful bugs has become a reality. Instead of chemical insecticides one has begun to use combating insects and for the pollination in the greenhouse bumble-bees, bees and the like, whose presence consequently is desirable and which represent a now negligible value so that their escape from the greenhouse must be prevented.
With regard to life conditions of the plants it is also absolutely necessary, that the greenhouse is ventilated, and for this purpose there exist sophisticated control systems, which control the opening and closing of the ventilator doors of the greenhouse. According to a known system the shutters are infintely controllable, which means that the air passage varies from fully open to closed. An insect-net to be used for this purpose must consequently be able to cover the whole opening, but on the other hand at reduced opening should not be able to blow out through this. In order to prevent the opening the insect-net along its whole length and width has to be controlled, which can be carried out by means of wires, rods or the like, but also assumes that the net is prepared, i.e. is reinforced where the strains are largest. The net consequently is subjected to appreciable mechanical strains, and an important requirement is that the net can resist these stresses without the net meshes being deformed. These are dimensioned after the smallest occurring insect and even a moderate deformation of the net meshes entails that the net does not fulfil its function.
The ventilation in greenhouses is carried out by self draught, which means, that the insect-net air permeability must be maximum, at the same time as the free opening of the net meshes must be very small, with regard to the smallest ocurring insect (the area of the net mesh should be in the magnitude of 0,5.times.0,5 mm). Besides the yarn in the net shall have the required strength, which also sets limits. An additional very important criterion which has to be complied with is that the woven net is step secure, by which is meant that the fabric is deformation resistant against dislocation of both crossing thread systems of the fabric (the warp and the weft). The step security is a special problem when thin yarnes must be used, which is unavoidable for insect-nets for greenhouses, since the net does not give too large shade effect. A light loss of one percent namely also implies one percent fall in production.
Since the insect-net is exposed to direct sunlight, the yarn material has to be UV-stable. Even there the thickness of the yarn comes into play, the thinner the yarn the poorer is also their UV-stability. This demand also strongly limits the material choice.
The object of the invention is to provide an insect-net of type mentioned by of introduction, which fulfills the following criteria:
1. Good UV-stability, even in relationship to the slight yarn thickness; PA1 2. High strength and long life-span; PA1 3. Slight yarn thickness in relation to the free hole in the net mesh, i.e. smallest possible of the yarn covered area relatively the open area; PA1 4. High air permeability (smallest possible pressure drop); PA1 5. Step secure, ie. deformation resistant against dislocation of the crossing thread system of the fabric; PA1 6. Drapeable or foldable, so that the insect-net occupies as small space as possible, when it is not used; PA1 7. The reinforcements for receiving control means for control of the insect-net must neither open the net meshes nor diminish their air permeability; PA1 8. Free of preparation, the insect-net shall be able to be manufactured without subsequent preparing, as that it directly fits for cooperation with the control means; PA1 9. Easy to mount and PA1 10. Shall be able to be manufactured in high production machines and thereby to a moderate price. PA1 11. Dirt-repelling.
These tasks have according to the invention been solved by at least the yarns of one of the thread systems preferably the warp yarn, as well as the weft yarn is composed by mono filament yarn, and so called "hairy" yarn with thread ends protruding from this, for example spun yarn. In the warp or weft direction of the fabric at some the distance from each other control threads are inlaid, which are provided to by even intervals to form loops for receiving control means fixed at the shutter.